Koch Wendelin, Forcisi Sara, Lehmann Rainer, Schmitt-Kopplin Philippe
Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, German Research Center for Environment Health, Neuherberg D-85764, Germany; Chair of Analytical Food Chemistry, Technische Universität München, Freising-Weihenstephan D-85354, Germany; German Center for Diabetes (DZD), Munchen, Germany.
Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, German Research Center for Environment Health, Neuherberg D-85764, Germany; Chair of Analytical Food Chemistry, Technische Universität München, Freising-Weihenstephan D-85354, Germany; German Center for Diabetes (DZD), Munchen, Germany.
J Chromatogr A. 2014 Sep 26;1361:209-16. doi: 10.1016/j.chroma.2014.07.104. Epub 2014 Aug 13.
The application of ammonia acetate buffered liquid chromatography (LC) eluents is known to concomitantly lead to ion suppression when electrospray ionization mass spectrometry (ESI-MS) detection is used. In negative ESI mode, post column infusion of 2-(2-methoxyethoxy)ethanol (2-MEE) was shown in the literature to help to compensate this adverse effect occurring in reversed phase liquid chromatography mass spectrometry (RP-LC-MS) analyses. Here a setup of direct infusion and hydrophilic interaction chromatography (HILIC) post-column infusion experiments was established in order to investigate systematically the beneficial effects of 2-MEE. We demonstrate that, 2-MEE can help to improve ESI-MS sensitivity in HILIC too and reveal analyte structure specific behaviors. Our study indicates that 2-MEE especially improves ESI response for small and polar molecules. The ESI response of stable isotope labeled amino acids spiked into biological matrices increases up to 50-fold (i.e. D5-l-glutamic acid) when post column infusion of 2-MEE is applied. A non-targeted analysis of a pooled urine sample via HILIC-ESI-QTOF-MS supports this hypothesis. In direct infusion, the combined application of an ammonia acetate buffered solution together with 2-MEE results in an improved ESI response compared to a non-buffered solution. We observed up to 60-fold increased ESI response of l-lysine. We propose this effect is putatively caused by the formation of smaller ESI droplets and stripping of positive charge from ESI droplets due to evaporation of acetic acid anions. In summary, post-column infusion of 2-MEE especially enhances ESI response of small and polar molecules. Therefore it can be regarded as a valuable add-on in targeted or non-targeted metabolomic HILIC-MS studies since this method sets a focus on this molecule category.
已知在使用电喷雾电离质谱(ESI-MS)检测时,应用乙酸铵缓冲液相色谱(LC)洗脱液会同时导致离子抑制。在负电喷雾电离模式下,文献表明柱后注入2-(2-甲氧基乙氧基)乙醇(2-MEE)有助于补偿反相液相色谱-质谱(RP-LC-MS)分析中出现的这种不利影响。在此,建立了直接注入和亲水相互作用色谱(HILIC)柱后注入实验装置,以便系统地研究2-MEE的有益效果。我们证明,2-MEE也有助于提高HILIC中的ESI-MS灵敏度,并揭示分析物结构的特异性行为。我们的研究表明,2-MEE特别能提高对小分子和极性分子的ESI响应。当应用2-MEE柱后注入时,添加到生物基质中的稳定同位素标记氨基酸的ESI响应增加高达50倍(即D5-L-谷氨酸)。通过HILIC-ESI-QTOF-MS对混合尿液样本进行的非靶向分析支持了这一假设。在直接注入中,与非缓冲溶液相比,乙酸铵缓冲溶液与2-MEE的联合应用导致ESI响应得到改善。我们观察到L-赖氨酸的ESI响应增加了高达60倍。我们认为这种效应可能是由于形成了更小的ESI液滴以及由于乙酸根阴离子的蒸发而使ESI液滴上的正电荷被剥离所致。总之,2-MEE柱后注入特别增强了小分子和极性分子的ESI响应。因此,它可被视为靶向或非靶向代谢组学HILIC-MS研究中有价值的附加物,因为该方法专注于这一分子类别。